The conventional tire mounting-demounting machines usually comprise, as is known, a base, a wheel-holder table rotatably mounted on the base, a (column) support which is extended from the base and one or more tool support arms, such as the so-called mounting-demounting tool, and one or a pair of bead breaker rollers and the like.
Up to now, several demounting tools have been proposed, equipped (or not equipped) with respective anchoring device to a support arm.
The patent IT-1 342 902, for example, teaches a tire demounting machine equipped with device or tool for demounting a tire from a rim. The machine is equipped with a telescopic arm, vertical during use, which on its lower part supports a block intended to be laterally abutted against an edge of the rim of a tired wheel. The following are arranged at different levels at the block: an upper extractor lever and a lower bead breaker lever pivoted at the lower part of the block. The articulation between the extractor lever and the block occurs by means of a pair of “small connecting rods” of different length, pivoted at their upper portion to a respective intermediate position of the extractor lever and at their lower part, at two different levels, to the block, so as to define an articulated quadrilateral structure therewith and with the extractor lever. A first double-acting fluid operated linear actuator, being extended transversely to the telescopic arm, is set to command the extractor lever, and a second actuator commands the angular movement of the bead breaker lever. First, the bead breaker lever is actuated—this is forced against the bead of the tire in order to carry out the bead breaking. Once the bead breaking is completed, the actuator of the extractor lever is actuated, which is forced to penetrate between the edge of the rim and the bead of the tire close to the bead breaker lever. By reversing the movement direction of the actuator of the extractor lever, the latter is forced to move backward, taking the bead of the tire with it beyond the edge of the rim, so as to carry out the extraction thereof. Once extraction has occurred, both levers are moved back into rest position.
The patent EP-1 593 533 teaches a tire mounting-demounting machine equipped with a vertical arm, which on its lower part supports a mounting-demounting tool, to which an extraction lever is laterally articulated. The articulation of the extraction lever to the tool is achieved by means of an articulated quadrilateral and the lever is actuatable by a jack by means of a crank gear. The extraction tool carries out the bead breaking before the extractor lever is actuated.
As will be understood, the conventional extraction devices for tire mounting-demounting machines have rather complex structures and are thus costly; they also require suitably trained personnel for the correct use thereof.
The European patent application EP-2 233 325 teaches a tire assembling-release machine provided with a tool for dismounting a tire from a wheel rim.
The machine is provided with a vertical, in use, arm supporting a work head, an extracting lever pivoted to the work head, and a linear actuator, which protrudes downwards from an upper portion of the work head.
More particularly, the extracting lever is articulated to the work head by means of two connecting rods; the actuator, the extracting lever and the connecting rods forming an articulated quadrilateral structure.
Owing to such quadrilateral structure, upon operation of the actuator in one direction, the extracting lever is caused to move along a first insertion path, whereas should the actuator be operated in the opposite direction, the extracting lever is displaced along a second extraction path, which differs from the first insertion path.
The machine disclosed in EP-2 233 325 has a complex structure expensive to be manufactured.